Study Designs

Question 1

1. Blocked design: principle, dis-

/advantages

Answer 1

● Stimuli that belong together in one condition are grouped together: maintains cognitive
engagement. AB block design has two alternating conditions
+ more power= greater ability to detect a small but significant effect
+ relatively large BOLD signal change compared to baseline
- some events cannot be blocked because the task requires that they are unexpected and infrequent

Question 2

2. Event-related design and behaviorally

driven design: principles, dis-/advantages

Answer 2

Event-related design (erfMRI)
● Stimuli that belong to different conditions are intermingled, then separated for analysis.
+ can detect transient variations in hemodynamic response: allows temporal characterisation of BOLD signal changes (basically you can time it better)
+ wider range of experimental designs
+ more closely related to typical design structure of cognitive psychology experiments
+ less sensitive to head motion artifacts + can be used to assess practice effects

+ allows randomisation and different inter-stimulus intervals (ISI): reduces participant’s ability to predict what will happen next, maintains attention level
+ can use post-hoc methods to detect internal processes. The subjective perception of a state is not driven by the experimenter

Question 3

3. Comparison strategies: subtraction

method

Answer 3

Cognitive subtraction
● Comparison of brain activity in task which uses cognitive component versus baseline task
which doesn’t: from that, you infer which region is specialised
o Can only be meaningfully interpreted relative to baseline
o Useful in combination with blocked designs, allows simple modelling of BOLD
response with robust and reproducible results
o Depends on assumption that two tasks (experimental and baseline) can be found,
which differ only in terms of measurable cognitive processes
o Requires good cognitive theory about elements that comprise the task, and ideally
maximum similarity: baseline task choice will affect the data obtained.

Assumes :

Pure insertion (adding an extra component doesn’t affect operation of earlier components in the sequence).
● Problem:
o If pure insertion is violated: suggests interaction, leading to ambiguous data
interpretation.

Question 4

4. Computation & interpretation of

activation maps

Answer 4

to be done

Question 5

5. Example studies by Wagner et al. (1998)
   and Roefs / Trojano et al. (2018):
   hypothesis, FMRI design, control conditions

Answer 5

Wagner

Task:
Semantic processing task
deciding if a word is abstract or concrete
Non-semantic processing task
deciding if a word is printed in upper- or lowercase letters

Block design:
activation during performance of a semantic processing task was compared to that during a non-semantic processing task
identify regions that demonstrate differential activation during encoding conditions
🡪 directly compared the semantic and non-semantic processing conditions

Event-related design:
participants performed a single incidental encoding task
determine whether trial-by-trial differences in encoding activation predict subsequent memory for experiences even when the processing task was held constant

Results :

Ability to later remember a verbal experience is predicted by the magnitude of activation in left prefrontal and temporal cortices during that experience

Question 6

factorial design, parametric design,

conjunction analysis

Answer 6

Factorial Design Principle:
principle is to have the subject perform a task where the cognitive components are intermingled in one moment, and separated in another instance of the paradigm
assumption: linearity between BOLD resulting from conditions (otherwise some of the findings may be contaminated by non-predicted interactions)
very useful, when it comes to investigating cognitive interactions

Parametric design :
cognitive tasks can be performed at different difficulty levels
increasing the difficulty of a task is the basis of the parametric design
increase in BOLD effect associated with an increase in cognitive demand would imply a heavy association of a particular area to the intrinsic nature of the parameter being manipulated

Conjunction analysis:
approach is aimed at finding commonalities between conditions and allows for another angle of analysis: What is the common pattern of BOLD response present in the conditions analyzed
intersection of the BOLD responses can help to distinguish basic processes from the experiment

Question 7

Behaviour driven fMRI and mixed design

Answer 7

Mixed design
● Combination of block and erfMRI designs
+ can provide information about maintained versus transient neural activity during paradigm performance (can extract brain regions exhibiting either (a) item-related patterns of information processing, transient, or (b) task-related information processing, maintained)
- involves more assumptions
Behaviour-driven fMRI
● Resting state paradigm, similar properties to erfMRI
- design is dependent on each subject’s performance and inter-subject variability. Number of events per condition and consequent statistical power is largely unknown beforehand

Question 8

Mental Clock Test

Answer 8

fMRI used to explore the neural correlates of behaviourally controlled spatial imagery.
● Mental clock test
o Subjects asked to imagine pairs of time presented acoustically and judge which would present a greater angle on a clock face
Hypothesis: increase in neuronal activity reflected by BOLD signal in parietal lobes, bilaterally, during entire mental clock test (whole cortex analysed to assess coactivation of other regions)
MR hardware and interfaces
● 1.5 tesla, interscan temporal spacing of 5s
● Per functional time series: 5 resting volumes 100 (exp 1) or 72 (exp 2) acquisitions, during
which the imagery condition was periodically alternated with a control condition every 10
(exp 1) or 8 (exp 2) scans
● After functional acquisition: high resolution 3D dataset covering whole brain collected

Discussion
● Cortical activation during mental clock test: most prominent in posterior parietal lobes of both
hemispheres
o Confirmation of findings that certain imagery conditions produce increases in activity
in primary visual areas only to a small extent
● Reverse inference: activation of PFC associated with attentional demand involved in different
kinds of mental imagery and working memory tasks
o PFC strongly involved in processing of spatially coded material in imagery domain.